A. Detection of Leakage in Optical Fibers and Waveguide
Waveguides and optical fibers deliver optical energy from one point to another. In the medical field, optical energy is used for both diagnostic and therapeutic purposes. Waveguides and optical fibers are used to transmit optical energy from a source outside the body to a targeted area inside the body. In some procedures, such as laparoscopy, rigid scopes and optical delivery systems may be used; however, often there is a need for flexible optical fibers and guides to reach various organs and body cavities that may be less than ideally positioned, such as, by way of example, the kidneys.
A bent waveguide or optical fiber may lose its integrity or its light guiding capability when it is bent to access the desired body cavity or organ, thus risking exposure to adjacent exposed instruments or body parts as a result of optical leakage. The high-energy levels experienced with certain therapeutic treatments further increase the risk of injury to non-targeted tissue within the body.
Therefore, there is a need for an apparatus and method to accurately monitor optical leakage from a waveguide to increase the safety of laser treatments.
B. Optical Mating of Laser Sources to Different-Sized Optical Fibers and Waveguides
Coupling a waveguide to a medical laser source may involve adjustment of different parameters in order to safely and efficiently deliver a laser beam produced by a laser system to the distal end of the waveguide. Often, with medical solid state or gas lasers, a laser beam produced in a laser cavity runs in free space to a fiber port. At the fiber port, an optical fiber may be connected to the laser system through a variety of available optical connectors.
Typically, a medical laser system has a laser cavity which is configured to produce a laser beam which is delivered in free space to a fiber. At such fiber port, the laser beam is characterized, among other things, by a certain spot size, beam quality and power. The fiber port is configured to align a proximal end of an optical fiber to the laser beam. The laser beam then travels through the optical fiber to its distal end towards the targeted tissue. An efficient fiber port should be designed to minimize any deterioration in the beam quality and energy loss. In addition, in order to avoid energy leakage in the optical coupling area and along the optical fiber, the beam should be preferably designed to match the numerical aperture (NA) of the optical fiber. The fiber port may include a focal lens which is configured to focus an incident laser beam into the core section of the optical fiber.
In order to deliver a laser beam having a diameter d into an optical fiber having a diameter D, a fiber port is designed so as to focus the laser beam so that the laser beam diameter is smaller than the fiber diameter (d>D). The greater the difference between the laser beam diameter d and optical fiber diameter D, the greater becomes the acceptable tolerance of mechanical misalignment between the laser beam and optical fiber at the point of coupling. However, the ability of a focal lens at a fiber port to reduce the spot size of a laser beam is limited and is a function, among other things, of the original laser beam diameter, its divergence as it travels through free space and beam quality.
In order to deliver a laser beam into a small diameter fiber such as, for example, 230μ, prior art systems provide a tapered proximal-end fiber 630 as seen in FIG. 6. The tapered proximal-end fiber 630 includes a tapered section 631 and a parallel section 632. Each section has core areas 610 and 620 and clad areas 611 and 621, respectively. Fiber 630 has a main longitudinal axis A-A, and tapered section 631 defines an angle α relative to axis A-A. In this non-limiting example, tapered section 631 has a proximal end, having a diameter D1, facing a fiber port and a distal section having a diameter D2 which is coupled to an optical fiber section 632. A tapered section having, for example, D1 at about 365μ, is capable to deliver an incident laser beam, as characterized in prior art systems, into a 230μ fiber.
As can be seen, an exemplary incident ray R which enters tapered section 631 hits clad area 611 at an angle α and is reflected at the same angle. However, as a general rule, each time reflected ray R hits clad area 611 its relative angle is doubled. According to this example, after reflecting twice after impinging on clad area 611, the reflected ray R enters the parallel section 632 of the optical fiber having an angle of 4α relative to the clad area 621. According to this example, as long as the critical angle for total internal reflection inside parallel section 632 is greater than 4α, ray R may efficiently propagate down the optical fiber. As a general rule, the ray angle relative to the clad section is doubled each time the ray hits the clad area in tapered section 631. Therefore, the numerical aperture (NA) of section 632 limits the number of times a ray can hit the clad in tapered area 631 and still propagate down the optical fiber without leaking.
Once the accumulated angle, due to multiple reflections along tapered section 631 reaches and exceeds the critical angle for total internal reflection of the fiber section 632, energy will leak from the fiber. In other words, the NA of optical fiber 32 limits the acceptable length of tapered section 631 and its maximal proximal diameter D1. One option to deal with this to allow a greater number of rays to safely be propagated along section 632 without leaking is to increase the NA of the fiber. This requires more expensive fibers such as sapphire, germanium or crystal silica and this added expense poses a serious problem when the fiber is a single use, disposable fiber. However, even by using expensive fibers, beam rays having incident angles greater than the critical angle of a better fiber will eventually leak and risk causing harm to the patient and to any adjacent equipment. Therefore, in order to safely deliver a laser beam having a bigger spot size or a higher divergence, the prior art solution described above is insufficient. It is one of the aspects of the current invention to provide an improved optical fiber adaptor.